cortav  cortav.ct at [9215a9c850]

File cortav.ct artifact 4ed3bc7476 part of check-in 9215a9c850

# cortav specification
[*cortav] is a markup language designed to be a simpler, but more capable alternative to markdown. its name derives from the [>dict Ranuir words] [!cor] "writing" and [!tav] "document", translating to something like "(plain) text document".

	dict: http://ʞ.cc/fic/spirals/glossary

the cortav [!format] can be called [!cortavgil], or [!gil cortavi], to differentiate it from the reference implementation [!cortavsir] or [!sir cortavi].

%toc

## cortav vs. markdown
the most important difference between cortav and markdown is that cortav is strictly line-oriented. this choice was made to ensure that cortav was relatively easy to parse. so while a simple [`.ct] file may look a bit like a [`.md] file, in reality it's a lot closer to gemtext than any flavor of markdown.

however, the differences go much deeper. the most distinctive feature of cortav is that its syntax is strongly recursive. with markdown, you can apply at most one styling to any given block or span or text. with cortav, you can nest as many styles as you like, and you can style text in places markdown wouldn't ordinarily let you: within headings, inside link text, even in code listings if you absolutely insist (this needs to be turned on by a special directive before the listing in question, however).

this manual describes cortav exhaustively, but if you just want a quick reference on how markdown translates to cortav, look no further.

* [*headings]: cortav uses almost the same syntax for headings that markdown does, except it only allows the "ATX style" headings, with one or more hash characters at the start of the line. the only differences from markdown are:
** you can use the unicode section character [`§] instead of [`#] if you're feeling snobby
** you must put a space between the control sequence (the sequence of hashes or section symbols, in this case) and the title text. [`# title] creates a section with the heading text "title", but [`#title] creates a new section with no heading at all; instead, it gives the anonymous section the ID [`title]. and of course, you can combine the two: [`#ttl title] creates a section with the heading text "title" and the ID [`ttl]. what are IDs for? we'll get to that in a little bit
* [*paragraphs] are mostly the same as in markdown, except that a paragraph break occurs after every newline character, not every blank line. paragraphs can be indented by however many spaces you like; such indentation will be ignored. (tabs have a special meaning, however). in cortav, you can also explicitly mark a line of text as a paragraph by preceding it with a period character ([`.]), which is useful if you want to start a paragraph with text that would otherwise be interpreted specially.
* [*italic text] -- or rather, [!emphasized] text -- is written as [`\[!my spiffy italic text\]]. in cortav, these spans can be nested within other spans (or titles, or table cells, or…), and the starting and ending point is unambiguous.
* [*bold text] -- or rather, [*strong] text -- is written as [`\[*my commanding bold text\]].
* [*bold-italic text] -- or rather, [![*emphasized strong text]] -- has no specific notation. rather, you create it by nesting one span within the other, for instance: [`\[*[!my ostentatious bold-italic text\]]].
* [*links] are quite different from their markdown equivalents. cortav does not have inline links, as it is intended to be easily readable in both formatted and plain-text format, and long URLs rather disrupt the flow of reading. rather, a link tag is written with the notation [`\[>nifty-link my nifty link\]], where the word [`nifty-link] immediately following the arrow is an [!identifier] indicating the destination of the link. (instead of a greater-than sign, you can also use the unicode arrow symbol [`→].) if the identifier is the same as one you've assigned to a section, cortav produces a link within the document to that section. otherwise, it will look for a [!reference] to tell it the URI for the link. a reference is a key-value pair created by adding a line like [`nifty-link: https://zombo.com] [!indented by exactly one tab]. you can place this reference anywhere you like so long as it's in the same section; if you want to name a reference in another section, you have to prefix it with that section's ID, e.g. [`\[>spiffy-section.nifty-link my nifty link declared in a spiffy section\]].
* [*lists] use a different syntax from markdown. you can start a line with a [`*] to create an unordered list, or [`:] to create an ordered list; indentation doesn't matter. if you want to nest list items, instead of putting two spaces before the child item, you just add another star or colon. and of course, you can nest lists of different kinds within one another.
* [*horizontal rules] use roughly the same syntax: three or more hyphens on a line of their own ([`\---]). underlines also work ([`___], [`-_-], [`__-__-__] etc).
* some markdown implementations support [*tables]. cortav does too, using a very simple notation.
* [*underlines] are supported by some markdown implementations. in cortav, you can apply them with the notation [`\[_my underlined text\]] -- please just use them sparingly when you render to HTML!
* [*strikethrough] is supported by some extended versions of markdown. cortav uses the notation [`\[~my deleted text\]], with the intended semantics of text that is being removed by some revision of a document. (you can also denote text that is being [!added] by using a plus sign instead of a tilde)
* [*images] are a bit more complicated. see the section on [>rsrc resources] for an explanation.
* [*smart quotes] and [*em dashes] are inserted automatically, just as in markdown, provided you have the [>tsmog transmogrify] extension available. (it is part of the reference implementation and defined by the spec, but not required.) in fact, you can insert longer dashes than em dashes just by increasing the number of hyphens. the reference implementation's transmogrifier also translates ascii arrows like [`\-->] into their unicode equivalents ([`→]).
* [*literals] (also known as [*code text]) can be inserted with the [`\[`int main(void);] syntax. note however that literals are not protected from the transmogrifier, and are parsed like any other span, which may cause problems if the source code you're quoting makes use of such forbidden runes. in this case, you'll want to wrap the code span in a raw span. the syntax for this is [`\[`[\\int main(void);\]]], but since this is a bit unwieldy it can also be abbreviated as [`\[`\\int main(void);\]].

of course, this is only a small taste of what cortav can do, not even touching on key features like macros, footnotes, or equation formatting. read the sections on [>onblocks blocks] and [>onspans spans] for all the gory details.

## encoding
a cortav document is made up of a sequence of codepoints. UTF-8 must be supported, but other encodings (such as UTF-32 or C6B) may be supported as well. lines will be derived by splitting the codepoints at the linefeed character or equivalent. note that unearthly encodings like C6B or EBCDIC will need to select their own control sequences.

## file type
a cortav source file is identified using a file extension, file type, and/or magic byte sequence.

three file extensions are defined as identifying a cortav source file. where relevant, all must be recognized as indicating a cortav source file.
* [`ct] is the shorthand extension
* [`cortav] is the canonical disambiguation extension, for use in circumstances where [`*.ct] is already defined to mean a different file format.
* [`] is the canonical Corran extension, a byte sequence comprising the unicode codepoints [`U+E3CE U+E3BD]. where the filesystem in question does not specify a filename encoding, the bytes should be expressed in UTF-8.

three more extensions are reserved for identifying a cortav intent file.
* [`ctc] is the shorthand extension
* [`cortavcun] is the canonical disambiguation extension
* [`] is the canonical Corran extension, a byte sequence comprising the unicode codepoints [`U+E3CE U+E3BD U+E3CE]. where the filesystem in question does not specify a filename encoding, the bytes should be expressed in UTF-8.

on systems which use metadata to encode filetype, two values are defined to identify cortav source files
* [`text/x-cortav] should be used when strings or arbitrary byte sequences are supported
* [`CTAV] (that is, the byte sequence [`0x43 54 41 56]) should be used on systems that support only 32-bit file types/4-character type codes like Classic Mac OS.

two more values are defined to identify cortav intent files.
* [`text/x-cortav-intent]
* [`CTVC] (the byte sequence [`0x43 54 56 43])

on systems which do not define a canonical way of encoding the filetype but support extended attributes of some kind, such as linux, an attribute named [$mime] may be created and given the value [`text/x-cortav] or [`text/x-cortav-intent]; alternatively, extensions may be used.

it is also possible to indicate the nature of a cortav file without using filesystem metadata. this is done by prefixing the file with a magic byte sequence. the sequence used depends on the encoding.
* for UTF-8 and ASCII plain text files, [`%ct[!\\n]] (that is, the byte sequence [`0x25 63 74 0A]) should be used
* for C6B+PS files (parastream), the file should begin with the paragraph [`], which equates to the byte sequence [` 0x3E 2E 14 0C 01 04 00 00 00 03 07 3E 2D], including the parastream header).
consequently, this sequence should be ignored by a cortav parser at the start of a file (except as an indication of file format).

for FreeDesktop-based systems, the [`build/velartrill-cortav.xml] file included in the repository supplies mappings for the extensions and magic byte sequences. a script is also included which can be registered with xdg-open so that double-clicking on a cortav file will render it out and open it in your default web browser. [`$ make install] will generate the necessary FreeDesktop XML files and register them, as well as install the script and the [`cortav] executable itself. for more information see [>refimpl-build building the reference implementation].

##onblocks structure
cortav is based on an HTML-like block model, where a document consists of sections, which are made up of blocks, which may contain a sequence of spans. flows of text are automatically conjoined into spans, and blocks are separated by one or more newlines. this means that, unlike in markdown, a single logical paragraph [*cannot] span multiple ASCII lines. the primary purpose of this was to ensure ease of parsing, but also, both markdown and cortav are supposed to be readable from within a plain text editor. this is the 21st century. every reasonable text editor supports soft word wrap, and if yours doesn't, that's entirely your own damn fault.

the first character(s) of every line (the "control sequence") indicates the role of that line. if no control sequence is recognized, the line is treated as a paragraph. the currently supported control sequences are listed below. some control sequences have alternate forms, in order to support modern, readable unicode characters as well as plain ascii text.

* [*paragraphs] ([`.] [` ¶] [`❡]): a paragraph is a simple block of text. the period control sequence is only necessary if the paragraph text starts with text that would be interpreted as a control sequence otherwise
* newlines [` \\]: inserts a line break into previous paragraph and attaches the following text. mostly useful for poetry or lyrics
* [*section starts] [`#] [`§]: starts a new section. all sections have an associated depth, determined by the number of sequence repetitions (e.g. "###" indicates depth-three"). sections may have headers and IDs; both are optional. IDs, if present, are a sequence of raw-text immediately following the hash marks. if the line has one or more space character followed by styled-text, a header will be attached. the character immediately following the hashes can specify a particular type of section. e.g.:
** [`#] is a simple section break.
** [`#anchor] opens a new section with the ID [`anchor].
** [`# header] opens a new section with the title "header".
** [`#anchor header] opens a new section with both the ID [`anchor] and the title "header".
** [`#>conversation] opens a blockquote section named [`conversation] without a header.
** [`#&id mime] opens a new inline object [`id] of type [`mime]. useful for embedding SVGs. the ID and mime type must be specified.
* [*nonprinting sections] ([`^]): sometimes, you'll want to create a namespace without actually adding a visible new section to the document. you can achieve this by creating a [!nonprinting section] and defining resources within it. nonprinting sections can also be used to store comments, notes, or other information that is useful to have in the source file without it becoming a part of the output
* [*resource] ([`@]): defines a [!resource]. a resource is an file or object that exists outside of the document but which will be included in the document somehow. common examples of resources include images, videos, iframes, or headers/footers. see [>rsrc resources] for more information.
* [*lists] ([`*] [`:]): these are like paragraph nodes, but list nodes that occur next to each other will be arranged so as to show they compose a sequence. depth is determined by the number of stars/colons. like headers, a list entry may have an ID that can be used to refer back to it; it is indicated in the same way. if colons are used, this indicates that the order of the items is signifiant. :-lists and *-lists may be intermixed; however, note than only the last character in the sequence actually controls the depth type.
* [*directives] ([`%]): a directive issues a hint to the renderer in the form of an arbitrary string. directives are normally ignored if they are not supported, but you may cause a warning to be emitted where the directive is not supported with [`%!] or mark a directive critical with [`%!!] so that rendering will entirely fail if it cannot be parsed.
* [*comments] ([`%%]): a comment is a line of text that is simply ignored by the renderer.
* [*asides] ([`!]): indicates text that diverges from the narrative, and can be skipped without interrupting it. think of it like block-level parentheses. asides which follow one another are merged as paragraphs of the same aside, usually represented as a sort of box. if the first line of an aside contains a colon, the stretch of styled-text from the beginning to the aside to the colon will be treated as a "type heading," e.g. "Warning:"
* [*code] ([`~~~]): a line beginning with ~~~ begins or terminates a block of code. code blocks are by default not parsed, but parsing can be activated by preceding the code block with an [`%[*expand]] directive. the opening line should look like one of the below
** [`~~~]
** [`~~~ language] (markdown-style shorthand syntax)
** [`~~~ \[language\] ~~~] (cortav syntax)
** [`~~~ \[language\] #id ~~~]
** [`~~~ title ~~~]
** [`~~~ title \[language\] ~~~]
** [`~~~ \[language\] title ~~~]
** [`~~~ title \[language\] #id ~~~]
*[*reference] (tab): a line beginning with a tab is treated as a "reference." references hold out-of-line metadata for preceding text like links and footnotes. a reference consists of an identifier followed by a colon and an arbitrary number of spaces or tabs, followed by text. whether this text is interpreted as raw-text or styled-text depends on the context in which the reference is used. in encodings without tab characters, two preceding blanks can be used instead.
* [*quotation] ([`<]): a line of the form [`<[$name]> [$quote]] denotes an utterance by [$name].
* [*blockquote] ([`>]): alternate blockquote syntax. can be nested by repeating the [`>] character.
* [*subtitle] ([`--]): attaches a subtitle to the previous header
* [*embed] ([`&]): embeds a referenced object. can be used to show images or repeat previously defined objects like lists or tables, optionally with a caption.
** [`&$[$macro] [$arg1]|[$arg2]|[$argn]…] invokes a block-level macro with the supplied arguments
*** [`&$mymacro arg 1|arg 2|arg 3]
** [`&[$image]] embeds an image or other block-level object. [!image] can be a reference with a url or file path, or it can be an embed section (e.g. for SVG files)
***[`&myimg All that remained of the unfortunate blood magic pageant contestants and audience (police photo)]
** [`&-[$section] [$styled-text]] embeds a closed disclosure element. in interactive outputs, this will display as a block [!section] which can be clicked on to view the full contents of the referenced section; if [$styled-text] is present, it overrides the title of the section you are embedding. in static outputs, the disclosure object will display as an enclosed box with [$styled-text] as the title text
*** [`&-ex-a Prosecution Exhibit A (GRAPHIC CONTENT)]
** [`&+[$section] [$styled-text]] is like the above, but the disclosure element is open by default
* [*horizontal rule] ([`\---]): inserts a horizontal rule or other context break; does not end the section. must be followed by newline. underlines can also be used in place of dashes.
* [*page break] ([`\^^]): for formats that support pagination, like HTML (when printed), indicates that the rest of the current page should be blank. for formats that do not, extra margins will be inserted. does not create a new section
* [*page rule] ([`\^-^]): inserts a page break for formats that support them, and a horizontal rule for formats that do not. does not create a new section
* [*table cells] ([`+ |]): see [>ex.tab table examples].
* [*equations] ([`=]) block-level equations can be inserted with the [`=]
* [*empty lines] (that is, lines consisting of nothing but whitespace) constitute a [!break], which terminates multiline objects that do not have a dedicated termination sequence, for example lists and asides.

##onspans styled text
most blocks contain a sequence of spans. these spans are produced by interpreting a stream of [*styled-text] following the control sequence. styled-text is a sequence of codepoints potentially interspersed with escapes. an escape is formed by an open square bracket [`\[] followed by a [*span control sequence], and arguments for that sequence like more styled-text. escapes can be nested.

* strong {obj *|styled-text}: causes its text to stand out from the narrative, generally rendered as bold or a brighter color.
* emphatic {obj !|styled-text}: indicates that its text should be spoken with emphasis, generally rendered as italics
* custom style {span .|id|[$styled-text]}: applies a specially defined font style. for example, if you have defined [`caution] to mean "demibold italic underline", cortav will try to apply the proper weight and styling within the constraints of the current font to the span [$styled-text]. see the [>fonts-sty fonts section] for more information about this mechanism.
* literal {obj `|styled-text}: indicates that its text is a reference to a literal sequence of characters or other discrete token. generally rendered in monospace
* variable {obj $|styled-text}: indicates that its text is a stand-in that will be replaced with what it names. generally rendered in italic monospace, ideally of a different color
* underline {obj _|styled-text}: underlines the text. use sparingly on text intended for webpages -- underlined text  [!is] distinct from links, but underlining non-links is still a violation of convention.
* strikeout {obj ~|styled-text}: indicates that its text should be struck through or otherwise indicated for deletion
* insertion {obj +|styled-text}: indicates that its text should be indicated as a new addition to the text body.
** consider using a macro definition [`\edit: [~[#1]][+[#2]]] to save typing if you are doing editing work
* link \[>[!ref] [!styled-text]\]: produces a hyperlink or cross-reference denoted by [$ref], which may be either a URL specified with a reference or the name of an object like an image or section elsewhere in the document. the unicode characters [`→] and [`🔗] can also be used instead of [`>] to denote a link.
* footnote {span ^|ref|[$styled-text]}: annotates the text with a defined footnote. in interactive output media [`\[^citations.qtheo Quantum Theosophy: A Neophyte's Catechism]] will insert a link with the next [`Quantum Theosophy: A Neophyte's Catechism] that, when clicked, causes a footnote to pop up on the screen. for static output media, the text will simply have a superscript integer after it denoting where the footnote is to be found.
* superscript {obj '|[$styled-text]}
* subscript {obj ,|[$styled-text]}
* raw {obj \\ |[$raw-text]}: causes all characters within to be interpreted literally, without expansion. the only special characters are square brackets, which must have a matching closing bracket
* raw literal \[$\\[!raw-text]\]: shorthand for [\[$[\…]]]
* macro [`\{[!name] [!arguments]\}]: invokes a [>ex.mac macro], specified with a reference
* argument {obj #|var}: in macros only, inserts the [$var]-th argument. otherwise, inserts a context variable provided by the renderer.
* raw argument {obj ##|var}: like above, but does not evaluate [$var].
* term {obj &|name}, {span &|name|[$expansion]}: quotes a defined term with a link to its definition, optionally with a custom expansion of the term (for instance, to expand the first use of an acronym)
* inline image {obj &@|name}: shows a small image or other object inline. the unicode character [`🖼] can also be used instead of [`&@].
* unicode codepoint {obj U+|hex-integer}: inserts an arbitrary UCS codepoint in the output, specified by [$hex-integer]. lowercase [`u] is also legal.
* math mode {obj =|equation}: activates additional transformations on the span to format it as a mathematical equation; e.g. [`*] becomes [`×] and [`/] --> [`÷].
* extension {span %|ext|…}: invokes extension named in [$ext]. [$ext] will usually be an extension name followed by a symbol (often a period) and then an extension-specific directive, although for some simple extensions it may just be the plain extension name. further syntax and semantics depend on the extension. this syntax can also be used to apply formatting specific to certain renderers, such as assigning a CSS class in the [`html] renderer ([`\[%html.myclass my [!styled] text]]).
* critical extension {span %!|ext|…}: like [!extension], but will trigger an error if the requested extension is not available
* extension text {span %:|ext|styled-text}: like [!extension], but when the requested extension is not present, [$styled-text] wlil be emitted as-is. this is a better way to apply CSS classes, as the text will still be visible when rendered to formats other than HTML.
* inline comment {obj %%|...}: ignored. useful for editorial annotations not intended to be part of the rendered product.

	span: [` \[[*[#1]][$[#2]] [#3]\]]
	obj: [` \[[*[#1]][$[#2]]\]]

##tabs tables
tables are encoded using a very simple notation. any line that begins with a plus [`+] or bar [`|] denotes a table row. each plus or bar separates one column from the other: a plus opens a new header cell, a bar opens a new normal cell.

the alignment of a cell can be specified by placing colons at one edge or both edges of the given cell. a colon on the left ([`|: my table cell |]) indicates a left-aligned cell, a colon on right a right-aligned cell ([`| my table cell :|]), and a colon on both sides a centered cell ([`|: my table cell :|]). if you want to use a special character without it being eaten by the table parser, just put a backslash in from of it, e.g. [`| this cell \| contains a pipe \+ a plus sign [!and] ends with a colon \:|]. and of course, table cells are just normal spans -- they can contain any other kind of span formatting you like, such as links, emphasis, or footnotes.

no other features (like colspans or rowspans) are currently part of the spec but they will be added eventually (if i can figure out a decent way to implement them without creating a huge mess).

you can finish each row with a bar or plus character, but it's not necessary. only do it if you think it makes the source easier to read.

* [>ex.tab an example of table notation]

##ident identifiers
any identifier (including a reference) that is defined within a named section must be referred to from outside that section as [`[!sec].[!obj]], where [$sec] is the ID of the containing section and [$obj] is the ID of the object one wishes to reference.

##rsrc resources
a [!resource] represents content that is not encoded directly into the source file, but which is embedded by some means in the output. resources can either be [!embedded], in which case they are compiled into the final document itself, or they can be [!linked], in which case the final document only contains a URI or similar tag referencing the resource. not all render backends support both linking and embedding embedding, nor do all backends support all object types (for instance, [`groff] does not support video embedding.)

a resource definition is begun by line consisting of an [`@] sign and an [>ident identifier]. this line is followed by any number of parameters. a parameter is a line beginning with a single tab, a keyword, a colon, and a then a value. additional lines can be added to a parameter by following it with a line that consists of two tabs followed by the text you wish to add. (this is the same syntax used by references.) a resource definition is terminated by a break, or any line that does not begin with a tab

a resource definition in use looks like this:

~~~
this is a demonstration of resources
@smiley
	src: link image/webp http://cdn.example.net/img/smile.webp
		  link image/png file:img/smile.png
		  embed image/gif file img/smile.gif
	desc: the Smiling Man would like to see you in his office
here is the resource in span context [&smiley]
and here it is in block context:
&smiley
~~~

rendered as HTML, this might produce the following:

~~~
<style>
	.res-smiley {
		content: image-set(
			url(http://cdn.example.net/img/smile.webp) type(image/webp),
			url(img/smile.png) type(image/png),
			url(data:image/gif;base64,/* … */) type(image/gif)
		); /* this will actually be repeated with a -webkit- prefix */
	}
</style>
<p>this is a demonstration of resources</p>
<p>here is the resource in span context: <span class="res-smiley"></span></p>
<p>and here it is in block context:</p>
<div class=".res-smiley"></div>
~~~

note that empty elements with CSS classes are used in the output, to avoid repeating long image definitions (especially base64 inline encoded ones!)

### supported parameters
* [`src] (all): specifies where to find the file, what it is, and how to embed it. each line of [`src] should consist of three whitespace-separated words: embed method, MIME type, and URI.
** embed methods
*** [`local]: loads the resource at build time and embeds it into the output file. not all implementations may allow loading remote network resources at build time.
*** [`remote]: only embeds a reference to the location of the resource. use this for e.g. live iframes, dynamic images, or images hosted by a CDN.
*** [`auto]: embeds a reference in file formats where that's practical, and use a remote reference otherwise.
** MIME types: which file types are supported depends on the individual implementation and renderer backend; additionally, extensions can add support for extra types. MIME-types that have no available handler will, where possible, result in an attachment that can be extracted by the user, usually by clicking on a link. however, the following should be usable with all compliant implementations
*** [`image/*] (graphical outputs only)
*** [`video/*] (interactive outputs only)
*** [`image/svg+xml] is handled specially for HTML files, and may or may not be compatible with other renderer backends.
*** [`font/*] can be used with the HTML backend to reference a web font
*** [`font/woff2] can be used with the HTML backend to reference a web font
*** [`text/plain] (will be inserted as a preformatted text block)
*** [`text/css] (can be used when producing HTML files to link in an extra stylesheet, either by embedding it or referencing it from the header)
*** [`text/x-cortav] (will be parsed and inserted as a formatted text block; context variables can be passed to the file with [`ctx.[$var]] parameters)
*** any MIME-type that matches the type of file being generated by the renderer can be used to include a block of data that will be passed directly to the renderer.
** URI types: additional URI types can be added by extensions or different implementations, but every compliant implementation must support these URIs.
*** [`http], [`https]: accesses resources over HTTP. add a [`file] fallback if possible for the benefit of renderers/viewers that do not have internet access abilities.
*** [`file]: references local files. absolute paths should begin [`file:/]; the slash should be omitted for relative paths. note that this doesn't have quite the same meaning as in HTML -- [`file] can (and usually should be) used with HTML outputs to refer to resources that reside on the same server. a cortav URI of [`file:/etc/passwd] will actually result in the link [`/etc/passwd], not [`file:///etc/passwd] when converted to HTML. generally, you only should use [`http] when you're referring to a resource that exists on a different domain.
*** [`name]: a special URI used generally for referencing resources that are already installed on a target system and do not need to be embedded or linked, the name and type are enough for a renderer on another machine to locate the correct resource. this is useful mostly for [>fonts fonts], where it's more typical to refer to fonts that are installed on your system rather than providing paths to font files.
*** [`gemini]: accesses resources over the gemini protocol. currently you should really only use this for [`local] resources unless you're using the gemtext renderer backend, since nothing but gemini browsers are liable to support this protocol.
* [`desc]: supplies a narrative description of the resources, for use as an "alt-text" when the image cannot be loaded and for screenreaders.
* [`detail]: supplies extra narrative commentary that is displayed contextually, e.g. when the user hovers her mouse cursor over the embedded object.

note that in certain cases, full MIME types do not need to be used. say you're defining a font with the [`name] URI -- you can't necessary know what file type the system fonts on another computer are going to be. in this case, you can just write [`font] instead of [`font/ttf] or [`font/woff2] or similar. all cortav needs to know in this case is what abstract kind of object you're referencing.


##ctxvar context variables
context variables are provided so that cortav renderers can process templates. certain context variables are provided for by the standard. you can test for the presence of a context variable with the directive [`%[*when] ctx [$var]]. context variables are accessed with the [` \[#[$name]\]] span.

* {def cortav.file} the name of the file currently being rendered
* {def cortav.path} the absolute path of the file currently being rendered
* {def cortav.time} the current system time in the form [`[#cortav.time]]
* {def cortav.date} the current system date in the form [`[#cortav.date]]
* {def cortav.datetime} the current system date and time represented in the locale or system-standard manner (e.g. [`[#cortav.datetime]])
* {def cortav.page} the number of the page currently being rendered
* {def cortav.id} the identifier of the renderer
* {def cortav.hash} the SHA3 hash of the source file being rendered
	def: [*[#1]]:

on systems with environment variables, these may be accessed as context variables by prefixing their name with [`env.].

different renderers may provide context in different ways, such as from command line options or a context file. any predefined variables should carry an appropriate prefix to prevent conflation.

##fonts fonts
for output backends that support font specification, cortav provides a sophisticated font management system by means of the [!font stack].

when a document parse begins, the font stack is empty (unless a default font has already been loaded by an intent file).
when the font stack is empty, cortav does not include font specifications in its output, and thus will use whatever the default of the various rendering programs is.

to use fonts, we first have to define the fonts as [>rsrc resources].

~~~cortav
%% first, we create a new section to namespace the fonts
#^fonts
%% we then define each font as a resource
@serif
	src: auto font name:Alegreya
		embed  font/ttf file:project-fonts/alegreya.ttf
		link font/woff2 file:/assets/font/alegreya.woff2
		auto font name:Times New Roman
		auto font dit:TR/bold=TRB/italic=TRI/bold,italic=TRBI
@sans
	src: link font name:Alegreya Sans
		link font name:Open Sans
		link font name:sans-serif
~~~

here we have defined two font families, [`fonts.serif] and [`fonts.sans]. each contains a list of references to fonts which will be tried in order. for example, this could be translated into the following CSS:

~~~css
@font-face {
	font-family: "fontdef-serif";
	src: local("Alegreya"),
		url("data:font/ttf;base64,…") format("font/ttf"),
		url("/assets/font/alegreya.woff2") format("font/woff2"),
		local("Times New Roman");
}
@font-face {
	font-family: "fontdef-sans";
	src: local("Alegreya Sans"),
		local("Open Sans"),
		local("sans-serif");
}
~~~

there are two things that aren't super clear from the CSS, however. notice how we used [`auto] on a couple of those specs? this means it's up to the renderer to decide whether to link or embed the font. for html, a font specified by name can't really be embedded, but for some file formats, it can be. [`auto] lets us produce valid HTML while still taking advantage of font embedding in other formats.

now that we have our font families defined, we can use their identifiers with the [`%[*font]] directive to control the font stack. the first thing we need to do is push a new font context. there's two ways we can do this:
	fnd: [`%[*font] [#1]]
* {fnd dup} will create a copy of the current font context, allowing us to make some changes and then revert later with the {fnd pop} command. this isn't useful in our case, however, because right now the stack is empty; there's nothing to duplicate.
* {fnd new} will create a brand new empty context for us to work with and push it to the stack. this can also be used to temporarily revert to the system default fonts, and then switch back with {fnd pop}.
* {fnd set} changes one or more entries in the current font context. it can take a space-separated list of arguments in the form [`[$entry]=[$font-id]]. the supported entries are:
** [`body]: the fallback font. if only this is set in a given font context, it will be used for everything
** [`paragraph]: the font used for normal paragraphs
** [`header]: the font used in headers
** [`subtitle]: the font used in subtitles
** [`list]: the font used in lists
** [`table]: the font used in tables
** [`caption]: the font used for captions
* {fnd pop} removes the top context from the font stack.

note that extensions may consult the font context for their entries specific to them. for instance, [>toc toc] checks for [`toc] before falling back to [`body] and then the default font.

these commands are enough to give us a very flexible setup. consider the following:

~~~cortav
%% let's pretend we've also defined the fonts 'title', 'cursive', and 'thin'

%font new
%font set body=sans header=serif
%font dup
%font header=title
# lorem ipsum dolor
%font pop

%% we've now set up a default font context, created a new context for the title of the
%% document, and then popped it back off after the title was inserted so that our
%% first font context is active again. everything after that last '%font pop' will
%% be printed in sans, except for headers, which will be printed in 'serif'

lorem ipsum dolor sit amet, sed consectetur apiscing elit…

%font dup
%font set body=cursive
> sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
> Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut
%font pop

%% above we created a blockquote whose text is printed in a cursive font; afterwards,
%% we simply remove this new context—

and everything is back the way it was at "lorem ipsum"

%% the font mechanism is at its most powerful when used with multiline macros:

	cursive-quote: %font dup
		%font set body=cursive
		> [#1]
		%font pop

%% now, whenever we want a block with a cursive body, we can simply invoke

&$cursive-quote Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident

%% without affecting the overall font context. in fact, since 'cursive-quote' creates
%% its context using 'dup', it would import all font specifications besides 'body'
%% from the environment it is invoked in
~~~

you may have noticed the rather odd bit at the end of our font definition, with the [`dit] URI. the reasons for this are tragic. groff, while delightful, has a thoroughly antiquated understanding of fonts, and doesn't support normal font formats like truetype. groff ships with a limited number of fonts in its own format, identified by obscurantist letter code ([`HBI] is "Helvetica Bold Italic", for instance) and lacking normal metadata. for this reason, you'll have to tell cortav how you want your fonts translated.

it is possible to use modern fonts with groff, but to do that you'll have to convert and install them, which is outside the scope of this document. however, even if you do this, you should specify a fallback font (if possible) so that people rendering your document on other machines still get somewhat sensible output.

the syntax of a [`dit] specification is [`dit:[$regular]], where [$regular] specifies the name of the regular font. this can be followed by any number of variant specifications [`/[$variant]=[$name]], where [$variant] is one of the tags described in the [>fonts-sty custom] style section, and [$name] is the name of a DIT font. so the URI in the example names a font [`T] with bold [`TB], italic [`TI], and bold-italic [`TBI].

the [`groff] backend does do a little magic to make this mess more bearable, however. some of groff's built-in fonts can be accessed by a [`name] URI instead of having to construct them by hand with a [`dit] URI -- the backend hardcodes metadata for these fonts so that documents can render somewhat intellgibly in groff even if the original author did not make special provisions for this. the groff fonts accessible by [`name] are:
* Times New Roman
* Helvetica
* Courier
* Bookman
additionally, as a shortcut, if the regular, bold, italic, and bold-italic variants of a DIT font have the predictable pattern of [`[$X]], [`[$X]B], [`[$X]I], [`[$X]BI] (which many do), you can simply write the URI [`dit:[$X]] and cortav will infer the rest. so the example above could be rewritten as [`dit:T] to exactly the same effect.

###fonts-sty custom styles
sometimes you want to be able to issue more specific formatting instructions than "italic" or "bold". cortav provides a simple [!custom style] mechanism to allow this. a custom style is simply a reference that binds a name to a sequence of space-separated formatting directives. these directives include:
* [`regular]: applies the regulat form of the font, overriding any previous set styles
* [`medium]: applies a weight of the font between [`regular] and [`bold], defaulting to [`regular] if one is not available
* [`demibold]: applies a weight of the font between [`regular] and [`bold], defaulting to [`bold] if one is not available
* [`bold]: applies the usual "bold" weight of the font
* [`dense]: applies the heaviest available weight of th the font. usually the same as [`bold]
* [`light]: applies the usual "light" weight of the font. most fonts do not have a light weight, so this will be the same as [`regular].
* [`thin]: applies the slimmest available weight of the font. usually the same as [`light].
* [`underline]: underlines the text
* [`strike]: strikes the text out
* [`italic]: applies a slanted variant of the font
* [`oblique]: applies the most slanted variant of the font available. usually the same as [`italic]
* [`font=[$id]]: switches to font [$id] for the duration of the span. [$id] must be the ID of a resource defining a font.
* [`[$ext].[$prop]=[$word]]: attaches extra information for use by formatting extensions. [$ext] must be the ID of the extension.

once a custom style is defined, you can make use of it using the [` \[.[$id] [$styled-text]\]] span notation, where [$id] is the identifier of the reference containing your style. for instance, to define and use a style named [`important] that [^pls-no specifies a dense, underlined variant of font [`impact]] and applies the CSS class [`blink] when rendered with the [`html] backend:
	pls-no: please do not do this
~~~cortav
this paragraph contains some [.important truly important] information.
	important: dense underline font=impact html.class=blink
~~~
you should always give your styles semantic names where practicable, instead of simply describing their graphical characteristics. this is good practice in general, but especially because your document will be renderable to different formats with different characteristics, and what makes text look important on a manpage in the terminal may be quite different from how it looks in a webpage or PDF.

##dir directives
	d: [`%[*[##1]]]
* {d author} encodes document authorship. multiple author directives can be issued to add additional coauthors
* {d cols} specifies the number of columns the next object should be rendered with
* {d include} transcludes another file
* {d import} reads in the contents of another file as an embeddable section
* {d quote} transcludes another file, without expanding the text except for paragraphs 
* {d embed}, where possible, embeds another file as an object within the current one. in HTML this could be accomplished with e.g. an iframe.
* {d expand} causes the next object (usually a code block) to be fully expanded when it would otherwise not be
* {d font} controls the font stack, for outputs that support changing fonts. see [>fonts fonts] for more information.
* {d lang} changes the current language, which is used by extensions to e.g. control typographical conventions, and may be encoded into the output by certain renderers (e.g. HTML). note that quotes and blockquotes can be set to a separate language with a simpler syntax. the language should be notated using IETF language tags
** {d lang is x-ranuir-Cent-CR8} sets the current language to Ranuir as spoken in the Central Worlds, written in Corran and encoded using UTF-8. this might be used at the top of a document to set its primary language.
** {d lang push gsw-u-sd-chzh} temporarily switches to Zürich German, e.g. to quote a German passage in an otherwise Ranuir document
** {d lang sec en-US} switches to American English for the duration of a section. does not affect the language stack.
** {d lang pop} drops the current language off the language stack, returning to whatever was pushed or set before it. this would be used, for instance, at the end of a passage
* {d pragma} supplies semantic data about author intent, the kind of information the document contains and hints about how it should be displayed to the user. think of them like offhand remarks to the renderer -- there's no guarantee that it'll pay any attention, but if it does, your document will look better. pragmas have no scope; they affect the entire document. the pragma function exists primarily as a means to allow parameters that would normally need to be specified on e.g. the command line to be encoded in the document instead in a way that multiple implementations can understand. a few standard pragmas are defined.
** {d pragma layout} gives a hint on how the document should be layed out. the first hint that is understood will be applied; all others will be discarded. standard hints include:
*** [`essay]
*** [`narrative]
*** [`screenplay]: uses asides to denote actions, quotes for dialogue
*** [`stageplay]: uses asides to denote actions, quotes for dialogue
*** [`manual]
*** [`glossary]
*** [`news]
*** [`book]: section depths 1-3 gain additional semantics
***: [*part]: the section gets a page to itself to announce the beginning of a new part or appendix
***: [*chapter]: the section is preceded by a page break
***: [*heading]: the section can occur on the same page as text and  headings from other sections
** {d pragma accent} specifies an accent hue (in degrees around the color wheel) for renderers which support colorized output
** {d pragma accent-spread} is a factor that controls the "spread" of hues used in the document. if 0, only the accent color will be used; if larger, other hues will be used in addition to the primary accent color.
** {d pragma dark-on-light on\|off} controls whether the color scheme used should be light-on-dark or dark-on-light
** {d pragma page-width} indicates how wide the pages should be
** {d pragma title-page} specifies a section to use as a title page, for renderer backends that support pagination

! note on pragmata: particularly when working with collections of documents, you should not keep formatting metadata in the documents themselves! the best thing to do is to have a makefile for compiling the documents using whatever tools you want to support, and encoding the rendering options in this file (for the reference implementation this currently means as command line arguments, but eventually it will support intent files as well) so they can all be changed in one place; pragmas should instead be used for per-document [*overrides] of default settings.
! a workaround for the lack of intent files in the reference implementation is to have a single pseudo-stylesheet that contains only {d pragma} statements, and then import this file from each individual source file using the {d include} directive. this is suboptimal and recommended only when you need to ensure compatibility between different implementations.
! when creating HTML files, an even better alternative may be to turn off style generation entirely and link in an external, hand-written CSS stylesheet. this is generally the way you should compile sources for existing websites if you aren't going to write your own extension.

##ex examples

~~~ blockquotes #bq [cortav] ~~~
the following excerpts of text were recovered from a partially erased hard drive found in the Hawthorne manor in the weeks after the Incident. context is unknown.

#>
—spoke to the man under the bridge again, the one who likes to bite the heads off the fish, and he suggested i take a brief sabbatical and journey to the Wandering Oak (where all paths meet) in search of inspiration and the forsaken sword of Pirate Queen Granuaile. a capital idea! i shall depart upon the morrow, having honored the Lord Odin and poisoned my accursed minstrels as is tradition—
—can't smell my soul anymore, but that's beside the point entirely—
—that second moon (always have wondered why nobody else seems to notice the damn fool thing except on Michaelmas day). alas, my luck did not endure, and i was soon to find myself knee-deep in—
—just have to see about that, won't we!—
#

the nearest surviving relative of Lord Hawthorne is believed to be a wandering beggar with a small pet meerkat who sells cursed wooden trinkets to unwary children. she will not be contacted, as the officers of the Yard fear her.
~~~

~~~links & notes #lnr [cortav] ~~~
this sentence contains a [>zombo link] to zombo com. you can do anything[^any] at zombo com.
	zombo: https://zombo.com
	any: anything you want
~~~

~~~ macros #mac [cortav] ~~~
the ranuir word {gloss cor|writing}…
	gloss: [*[#1]] “[#2]”
~~~

~~~ tables #tab [cortav] ~~~
here is a glossary table.

+ english :+ ranuir + zia ţai  + thaliste        +
| honor   :| tef    | pang     | mbecheve        |
| rakewym :| hirvag | hi phang | nache umwelinde |
| eat     :| fese   | dzia     | rotechqa        |

and now the other way around!

+:english  :| honor |
+:ranuir   :| tef   |
+:zia ţai  :| pang  |
+:thalishte:| mbecheve |
~~~

##extns extensions
the cortav specification also specifies a number of extensions that do not have to be supported for a renderer to be compliant. the extension mechanism supports the following directives.

* inhibits: prevents an extension from being used even where available
* uses: turns on an extension that is not specified by the user operating the renderer (e.g. on the command line)
* needs: causes rendering to fail with an error if the extensions are not available

where possible, instead of [`needs [$x y z]], the directive [`when has-ext [$x y z]] should be used instead. this causes the next section to be rendered only if the named extensions are available. [`unless has-ext [$x y z]] can be used to provide an alternative format.

extensions are mainly interacted with through directives. all extension directives must be prefixed with the name of the extension.

the reference implementation seeks to support all standardized extensions. it's not quite there yet, however.

###toc toc
sections that have a title will be included in the table of contents. the table of contents is by default inserted at the break between the first level-1 section and the section immediately following it. you may instead place the directive [`toc] where you wish the TOC to be inserted, or suppress it entirely with [`inhibits toc]. note that some renderers may not display the TOC as part of the document itself.

toc provides the directives:

* [`%[*toc]]: insert a table of contents in the specified position. this can be used more than once, but doing so may have confusing, incorrect, or nonsensical results under some renderers, and some may just ignore the directive entirely
* [`%[*toc] mark [$styled-text]]: inserts a TOC entry with the label [$styled-text]  pointing to the current location. this can be used to e.g. mark noteworthy images, instances of long quotes or literal blocks, or functions inside an expanded code block.
* [`%[*toc] name [$id styled-text]]: like [`%[*toc] mark] but allows an additional [$id] parameter which specifies the ID the renderer will assign to an anchor element. this is not meaningful for all renderers and when it is, it is up to the renderer to decide what it means.
** the [*html] render backend interprets [$id] as the [`id] element for the anchor tag
** the [*groff] render backend ignores [$id]

###tsmog transmogrify
a cortav renderer may automatically translate punctuation marks or symbol sequences to superior representations depending on their context. to be compliant this extension should implement, at minimum:
* smart quotes (with consideration for the typographical conventions languages like German or Spanish)
** {dir.d transmogrify|language [$lang]} can be used to explicitly set the language; otherwise, it must be determined from the value of {dir.d pragma|lang}. if this is not present, implementations may fall back on their own methods for determining the language in use, such as command-line flags.
* multigraph to glyph conversion, including at least:
** [`\--] --> "—"
** [`\-->] --> "→"
** [`\<--] -->  "←"

an escape character before any of the sequence characters should prevent the sequence from being rendered. raw nodes (that is, [`\[\…\]] and [`\[`\…\]]) should not be scanned for transmogrification, nor should the contents of code blocks unless marked with the [`%[*expand]] directive

transmogrification shall only take place after all other parsing steps are completed.

###hilite hilite
code can be highlighted according to the formal language it is written in. a compliant hilite implementation must implement basic keyword, symbol, comment, pragma, and literal highlighing for the following formal languages.
* C
* [>lua Lua]
* [>html HTML]
* [>scheme Scheme]
* [>terra Terra]
* [>libconfig libconfig]

	lua: https://lua.org
	scheme: https://call-cc.org
	terra: https://terralang.org
	html: https://dev.w3.org/html5/spec-LC/
	libconfig: http://hyperrealm.github.io/libconfig/

the highlighter should make use of semantic HTML tags like [`<var>] where possible.

###lua lua
renderers with a lua interpreter available can evaluate lua code:
* [`%lua use [!file]]: evaluates [$file] and makes its definitions available
* [`\[%lua raw [!script]\]]: evaluates [$script] and emits the string it returns (if any) in raw span context.
* [` \[%lua exp [!script]\]]: evaluates [$script] and emits the string it returns (if any) in expanded span context.
* [`%lua raw [!script]]: evaluates [$script] and emits the string array it returns (if any) in raw block context.
* [`%lua exp [!script]]: evaluates [$script] and emits the string array it returns (if any) in expanded block context.

the interpreter should provide a [`cortav] table with the objects:
* [`ctx]: contains context variables

used files should return a table with the following members
* [`macros]: an array of functions that return strings or arrays of strings when invoked. these will be injected into the global macro namespace.

###ts ts
the [*ts] extension allows documents to be marked up for basic classification constraints and automatically redacted. if you are seriously relying on ts for confidentiality, make damn sure you start the file with [$%[*requires] ts], so that rendering will fail with an error if the extension isn't supported.

ts enables the directives:
* [`%[*ts] class [$scope level] ([$styled-text])]: indicates a classification level for either the while document (scope [$doc]) or the next section (scope [$sec]). if the ts level is below [$level], the section will be redacted or rendering will fail with an error, as appropriate. if styled-text is included, this will be treated as the name of the classification level.
* [`%[*ts] word [$scope word] ([$styled-text])]: indicates a codeword clearance that must be present for the text to render. if styled-text is present, this will be used to render the name of the codeword instead of [$word].
* [`%[*when] ts level [$level]]
* [`%[*when] ts word [$word]]

ts enables the spans:
* [`\[🔒#[!level] [$styled-text]\]]: redacts the span if the security level is below that specified.
* [`\[🔒.[!word] [$styled-text]\]]: redacts the span if the specified codeword clearance is not enabled.
(the padlock emoji is shorthand for [`%[*ts]].)

ts redacts spans securely; that is, they are simply replaced with an indicator that they have been redacted, without visually leaking the length of the redacted text.

~~~#ts-example example [cortav] ~~~
%ts word doc sorrowful-pines SORROWFUL PINES

# intercept R1440 TCT S3
this communication between the ambassador of [*POLITY DOORMAT CRIMSON] "Socialist League world Glory" and an unknown noble of [*POLITY ROSE] "the Empire of a Thousand Suns" was intercepted by [*SYSTEM SUPINE WARBLE].

## involved individuals
* (A) [*DOORMAT CRIMSON] Ambassador [🔒.morose-frenzy Hyacinth Autumn-Lotus] (confidence 1.0)
* (B) [*ROSE] Duchess [!UNKNOWN] (confidence 0.4)

## provenance
this communication was retrieved by [🔒#3 automated buoy downlink] from [*SYSTEM SUPINE WARBLE].

%ts level sec 9 ULTRAVIOLET
##> transcript
<A> we may have a problem
<B> Hyacinth, I told you not to contact me without—
<A, shouting> god DAMMIT woman I am trying to SAVE your worthless skin
<B> Hyacinth! your Godforsaken scrambler!
<A> …oh, [!fuck].
(signal lost)
~~~

#refimpl reference implementation
the cortav standard is implemented in [`cortav.lua], found in this repository. only the way [`cortav.lua] interprets the cortav language is defined as a reference implementation; other behaviors are simply how [`cortav.lua] implements the specification and may be copied, ignored, tweaked, violently assaulted, or used as inspiration by a compliant parser.

the reference implementation can be used both as a lua library and from the command line. [`cortav.lua] contains the parser and renderers, [`ext/*] contain various extensions, [`sirsem.lua] contains utility functions, and [`cli.lua] contains the CLI driver.

##refimpl-lib lua library
there are various ways to use cortav from a lua script; the simplest however is probably to precompile your script with luac and link in the necessary components of the implementation. for instance, say we have the following program

~~~ stdin2html.lua [lua] ~~~
local ct = require 'cortav'
local mode = {}
local doc = ct.parse(io.stdin, {file = '(stdin)'}, mode)
doc.stage = {
	kind = 'render';
	format = 'html';
	mode = mode;
}
output:write(ct.render.html(doc, {accent = '320'}))
~~~

and the only extension we need is the table-of-contents extension. our script can be translated into a self-contained lua bytecode blob with the following command

~~~
$ luac -s -o stdin2html.lc $cortav_repo/{sirsem,cortav,ext/toc}.lua stdin2html.lua
~~~

and can then be operated with the command [`lua stdin2html.lc], with no further need for the cortav repository files. note that the order of the [`luac] command is important! [`sirsem.lua] must come first, followed by [`cortav.lua], followed by any extensions. your driver script (i.e. the script with the entry point into the application) should always come last.

###refimpl-tools building custom tools
generally, most existing file-format conversion tools (cmark, pandoc, and so on) have a crucial limitation: they hardcode specific assumptions like document structure. this means that the files they output are generally not suitable as-is for the users' purposes, and require further munging, usually by hateful shell or perl scripts. some tools do provide libraries end users to use as a basis for designing their own tools, but these are often limited, and in any case the user ends up having to write their own (non-standard) driver. it's no surprise that very few people end up doing this.

[`cortav.lua]'s design lends itself to a more elegant solution. one can of course write their own driver using [`cortav] as a library, but most of the time when you're compiling document sources, you just want a binary you can run from the command line or a makefile. with [`cortav.lua], you can extend its capabilities easily while keeping the same driver.

in the [`cortav] spec, extensions are mostly intended to give different implementations the ability to offer extra capabilities, but the reference implementation uses an extension architecture that makes it easy to write and add your own. for each type of new behavior you want to implement, just create a new extension and list it on the make command line:

~~~
$ nvim ~/dev/my-cortav-exts/imperial-edict.lua
$ make cortav extens+=$HOME/dev/my-cortav-exts/*.lua
~~~

the cortav binary this produces will have all the extra capabilities you personally need, without any need to fork [`cortav.lua] itself or even touch the repository.

there's no reason [`cortav.lua] shouldn't be able to load extensions at runtime as well; i just haven't implemented this behavior yet. it probably would only take a few extra lines of code tho.

i will eventually document the extension API, but for now, look at [`ext/toc.lua] for a simple example of how to register an extension.

##refimpl-cli command line driver
the [$cortav.lua] command line driver can be run from the repository directory with the command [`lua ./cli.lua], or by first compiling it into a bytecode form that links in all its dependencies. this is the preferred method for installation, as it produces a self-contained executable which loads more quickly, but running the driver in script form may be desirable for development or debugging.

the repository contains a GNU makefile to automate compilation of the reference implementation on unix-like OSes. simply run [`$ make cortav] or [`$ gmake cortav] from the repository root to produce a self-contained bytecode executable that can be installed anywhere on your filesystem, with no dependencies other than the lua interpreter.

! note that the makefile strips debugging symbols to save space, so running [`cli.lua] directly as a script may be helpful if you encounter errors and need stacktraces or other debugging information.

henceforth it will be assumed that you have produced the [`cortav] executable and placed it somewhere in your [$$PATH]; if you are instead running [`cortav.lua] directly as an interpreted script, you'll need to replace [`$ cortav] with [`$ lua ./cli.lua] in incantations.

when run without commands, [`cortav.lua] will read input from standard input and write to standard output. alternately, a source file can be given as an argument. to write to a specific file instead of the standard output stream, use the [`-o [!file]] flag.

~~~
$ cortav readme.ct -o readme.html
	# reads from readme.ct, writes to readme.html
$ cortav -o readme.html
	# reads from standard input, writes to readme.html
$ cortav readme.ct
	# reads from readme.ct, writes to standard output
~~~

###refimpl-build building
the command line driver is built and installed with a GNU [$make] script. this script accepts the variables shown below with their default values:
+ prefix | [`[$$HOME]/.local] | the path under which the package will be installed
+ build | [`build] |  the directory where generated objects will be placed; useful for out-of-tree builds
+ bin-prefix | [`[$$prefix]/bin] | directory to install the executables to"
+ default-format-flags | [`-m html:width 35em] | a list of flags that will be passed by the viewer script to [`cortav] when generating a html fille

the following targets are supplied to automate the build:
* [`install] builds everything, installs the bytecode-executable and the viewer script to [$$bin_prefix], and registers the viewer script with XDG
* [`install-bin] is like [`install] but installs the binary version instead of the bytecode one
* [`excise] deletes everything installed and deregisters the file handlers (note that the same variables must be passed to [`exicse] as were passed to [`install]!)
* [`clean] deletes build artifacts from the [$$build] directory like it was never there
* [`wipe] is equivalent to [`$ make excise && make clean]

if you don't want to install [`cortav], you can just run [`$ make] without arguments to build the executable.

there are two different ways of building the driver. one is to generate a bytecode file that can be executed directly as a script. this is the most straightforward method, and requires only [`lua] and [`luac]. however, it has several substantial downsides: because it's only a bytecode file, it requires the [`lua] interpreter to run -- and in some environments, the security characteristics of the [`lua] interpreter may make this undesirable. it also must hardcode the path to the lua interpreter (though admittedly this is easy enough to fix if you copy it to another machine of the same architecture). [`lua] is not an entirely predictable environment, as it is controlled by environment variables and may hypothetically do things like load default libraries or alter paths in ways that disrupt the workings of [`cortav]. finally, because the bytecode file is not a binary executable, it cannot directly be given enhanced capabilities on unix-like systems through filesystem metadata -- SUID and caps will be ignored by the kernel. while this is of no importance in ordinary operation, there are niche cases where this could be troublesome.

a potentially superior alternative is to build [`cortav] as a directly executable binary. when you tell [`make] to build the binary version, it first compiles the driver to raw bytecode, then invokes [`tool/makeshim.lua] to create a C source file embedding that bytecode, which is then piped into a C compiler. the huge downside, of course, is that building the cortav driver in this way requires a C compiler. however, the binary that it produces is easier to distribute to other computers -- you can even statically link in lua so it can run on systems where lua isn't installed.

to build the binary version, run [`$ make build/cortav.bin]. if you want to make the build to link lua statically, you'll additionally need to supply lua's library prefix in the variable [`lua-lib-prefix]. some example  incantations:
* [`$ make build/cortav.bin lua-lib-prefix=/usr/lib] on most Linux distros
* [`$ make build/cortav.bin lua-lib-prefix=/usr/local/lib] on FreeBSD
* [`$ make build/cortav.bin lua-lib-prefix=$(nix path-info nixpkgs.lua5_3)/lib] on NixOS, or on OSX if you're using the Nix package manager

alternately, you can build lua yourself and link the static library in place without installing it systemwide, which is useful if you want to build a specialized version of lua to link with (or if the sysop doesn't want your grubby luser hands all over his precious filesystem). note that if you're building a self-contained version of [`cortav] to distribute, you may want to slim down the binary by building lua without its parser, as the self-contained version of the driver only needs the bytecode VM part of lua to run.

#### build variables
there are numerous variables you can use to control the build process.

+ lua | path to the lua interpreter [`cortav] should be built and run with
+ luac | path to the lua compiler
+ sh | path to a bourne-compatible shell
+ extens | list of paths to extensions to enable, defaults to [`ext/*.lua]. use [`extens\+=[$path]] to add additional extensions from out of tree
+ rendrs | list of paths to renderers to enable, defaults to [`render/*.lua]
+ build | path to the build directory, defaults to [`build]. change this for out-of-tree builds
+ executable | name of the executable to be generated, defaults to [`cortav]
+ default-format-flags | specifies command line options that the viewer script should pass to [`cortav]
+ prefix | where files should be installed, defaults to [`$HOME/.local]
+ bin-prefix | where executables should be installed, defaults to [`$(prefix)/bin]
+ debug | if set, builds executables with debugging symbols; if absent, executables are stripped
+ encoding-data | if set, embeds character class data for supported multibyte encodings into the program. on by default; [`$ make encoding-data=] to unset
+ encoding-data-ucs | path to the UnicodeData.txt file for UCS-based encodings like UTF-8. by default it is automatically downloaded with [`curl]
+ encoding-data-ucs-url | where to download UnicodeData.txt from, if encoding-data-ucs is not changed. defaults to the unicode consortium website

#### deterministic builds
some operating systems, like NixOS, require packages that can be built in reproducible ways. this implies that all data, all [!state] that goes into producing a package needs to be accounted for before the build proper begins. the [`cortav] build process needs to be slightly altered to support such a build process.

while the cortav specification itself does not concern itself with matters like whether a particular character is a numeral or a letter, optimal typesetting in some cases requires such information. this is the case for the equation span- and block-types, which need to be able to distinguish between literals, variables, and mathematical symbols in [^alas-math the equations they format]. the ASCII charset is small enough that exhaustive character class information can be manually hardcoded into a cortav implementation, the various encodings of Unicode most certainly are not.

	alas-math: sadly, i was not at any point consulted by any of the generations of mathematicians stretching back into antiquity who devised their notations without any regard for machine-readability. [!for shame!]

for this reason, the reference implementation of cortav embeds the file [`UnicodeData.txt], a database maintained by the Unicode Consortium. this is a rather large file that updates for each new Unicode version, so it is downloaded as part of the build process. to build on NixOS, you'll need to either disable the features that rely on this database (not recommended), or download the database yourself and tell the build script where to find it. this is the approach the official nix expression will take when i can be bothered to write it. see the examples below for how to conduct a deterministic build

~~~ deterministic build with unicode database [sh] ~~~
/src $ mkdir cortav && cd cortav
/src/cortav $ fossil clone https://c.hale.su/cortav .fossil && fossil open .fossil
/src/cortav $ curl https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt > /tmp/unicode.txt
/src/cortav $ make build/cortav encoding-data-ucs=/tmp/unicode.txt
~~~
~~~ [sh] deterministic build [!without] unicode database ~~~
/src $ mkdir cortav && cd cortav
/src/cortav $ fossil clone https://c.hale.su/cortav .fossil && fossil open .fossil
/src/cortav $ make build/cortav encoding-data=
~~~

! while most of the data used is taken directly from UnicodeData.txt, the database generated by [`tools/ucs.lua] splices in some extra character information before generating a database. this is partly because certain characters may not be classified in a useful way and need to be manually overwritten. however, the reference implementation also seeks to provide accurate data for certain character sets that are not part of unicode proper and can be expressed in UTF only through its private use areas.
! currently, only the [>corran Corran] script is currently supported in this fashion, but i intend to add [>tengwar Tengwar] as well. if there is a con-script or any other informally encoded script you would like supported by the reference implementation, please open an issue.

[*do note] that no cortav implementation needs to concern itself with character class data. this functionality is provided in the reference implementation strictly as an (optional) extension to the spec to improve usability, not as a normative requirement.

	corran: http://ʞ.cc/fic/spirals/society
	tengwar: https://en.wikipedia.org/wiki/Tengwar

###refimpl-switches switches
[`cortav.lua] offers various switches to control its behavior.
+ long                      + short + function                                    +
| [`--out [!file]]              :|:[`-o]:| sets the output file (default stdout)       |
| [`--log [!file]]              :|:[`-l]:| sets the log file (default stderr)          |
| [`--define [!var] [!val]]     :|:[`-d]:| sets the context variable [$var] to [$val]  |
| [`--mode-set [!mode]]         :|:[`-y]:| activates the [>refimpl-mode mode] with ID [!mode]
| [`--mode-clear [!mode]]       :|:[`-n]:| disables the mode with ID [!mode]           |
| [`--mode [!id] [!val]]        :|:[`-m]:| configures mode [!id] with the value [!val] |
| [`--mode-set-weak [!mode]]    :|:[`-Y]:| activates the [>refimpl-mode mode] with ID [!mode] if the source file does not specify otherwise
| [`--mode-clear-weak [!mode]]  :|:[`-N]:| disables the mode with ID [$mode] if the source file does not specify otherwise
| [`--mode-weak [!id] [!val]]   :|:[`-M]:| configures mode [$id] with the value [$val] if the source file does not specify otherwise
| [`--help]                     :|:[`-h]:| display online help                         |
| [`--version]                  :|:[`-V]:| display the interpreter version             |

###refimpl-mode modes
most of [`cortav.lua]'s implementation-specific behavior is controlled by use of [!modes]. these are namespaced options which may have a boolean, string, or numeric value. boolean modes are set with the [`-y] [`-n] flags; other modes use the [`-m] flags.

most modes are defined by the renderer backend. the following modes affect the behavior of the frontend:

+ ID                 + type   + effect
|   [`render:format]:| string | selects the [>refimpl-rend renderer] (default [`html])
| [`parse:show-tree]:| flag   | dumps the parse tree to the log after parsing completes

##refimpl-rend renderers
[`cortav.lua] implements a frontend-backend architecture, separating the parsing stage from the rendering stage. this means new renderers can be added to [`cortav.lua] relatively easily. currently, only an [>refimpl-rend-html HTML renderer] is included; however, a [`groff] backend is planned at some point in the future, so that PDFs and manpages can be generated from cortav files.

###refimpl-rend-html html
the HTML renderer is activated with the incantation [`-m render:format html]. it is currently the default backend. it produces a single HTML file, optionally with CSS styling data, from a [`.ct] input file.

####refimpl-rend-html-modes modes
[`html] supports the following modes:

* string (css length) [`html:width] sets a maximum width for the body content in order to make the page more readable on large displays
* number [`html:accent] applies an accent hue to the generated webpage. the hue is specified in degrees, e.g. [$-m html:accent 0] applies a red accent.
* flag [`html:dark-on-light] uses dark-on-light styling, instead of the default light-on-dark
* flag [`html:fossil-uv] outputs an HTML snippet suitable for use with the Fossil VCS webserver. this is intended to be used with the unversioned content mechanism to host rendered versions of documentation written in cortav that's stored in a Fossil repository.
* number [`html:hue-spread] generates a color palette based on the supplied accent hue. the larger the value, the more the other colors diverge from the accent hue.
* string [`html:link-css] generates a document linking to the named stylesheet
* flag [`html:gen-styles] embeds appropriate CSS styles in the document (default on)
* flag [`html:snippet] produces a snippet of html instead of an entire web page. note that proper CSS scoping is not yet implemented (and can't be implemented hygienically since [$scoped] was removed 😢)
* string [`html:title] specifies the webpage titlebar contents (normally autodetected from the document based on headings or directives)
* string [`html:font] specifies the default font to use when rendering as a CSS font specification (e.g. [`-m html:font 'Alegreya, Junicode, Georgia, "Times New Roman"])

~~~
$ cortav readme.ct --out readme.html \
	-m render:format html \
	-m html:width 40em \
	-m html:accent 80 \
	-m html:hue-spread 35 \
	-y html:dark-on-light # could also be written as:
$ cortav readme.ct -ommmmy readme.html render:format html html:width 40em html:accent 80 html:hue-spread 35 html:dark-on-light
~~~

#### directives
[`html] supplies the following render directives.

* [`%[*html] link [$rel] [$mime] [$href]]: inserts a [`<link>] tag in the header, for example, to link in an alternate stylesheet, or help feed readers find your atom or rss feed.
** [`%[*html] link alternate\\ stylesheet text/css /res/style2.css]
** [`%[*html] link alternate application/atom+xml /feed.atom]
* [`%[*html] style [$id]]: adds the stylesheet referenced by [$id] into the document stylesheet. the stylesheet is specified using a [>rsrc resource].

#### stylesheets
the [`html] backend offers some additional directives for external CSS files that are embedded into the document, in order to simplify integration with the accent mechanism. these are:

* [`@[*fg]]: resolves to a color expression denoting the selected foreground color. equivalent to [`[*tone](1)]
* [`@[*bg]]: resolves to a color expression denoting the selected background color. equivalent to [`[*tone](0)]
* [`@[*tone]\[/[$alpha]\]([$fac] \[[$shift] \[[$saturate]\]\] )]: resolves to a color expression. [$fac] is a floating-point value scaling from the background color to the foreground color. [$shift] is a value in degrees controlling how far the hue will shift relative to the accent. [$saturate] is a floating-point value controlling how satured the color is.

###refimpl-rend-groff groff
the [`groff] backend produces a text file suitable for supplying to a [`groff] compiler. [`groff] is the GNU implementation of a venerable typesetting system from the early days of UNIX

as a convenience, the groff backend supports two modes of operation: it can write a [`groff] file directly to disk, or it can automatically launch a [`groff] process with the appropriate command line options and environment variables. this second mode is recommended unless you're rendering very large files to multiple formats, as [`groff] invocation is nontrivial and it's best to let the renderer handle that for you.

####refimpl-rend-groff-modes modes
[`groff] supports the following modes:

* string [`groff:annotate] controls how footnotes will be handled.
** [`footnote] places footnotes at the end of the page they are referenced on. if the same footnote is used on multiple pages, it will be duplicated on each.
** [`secnote] places footnotes at the end of each section. footnotes used in multiple sections will be duplicated for each
** [`endnote] places all footnotes at the end of the rendered document.
* string [`groff:dev] names an output device (such as [`dvi] or [`pdf]). if this mode is present, [`groff] will be automatically invoked
* string [`groff:title-page] takes an identifier that names a section. this section will be treated as the title page for the document.

### directives
* [`%[*pragma] title-page [$id]] sets the title page to section [$id]. this causes it to be specially formatted, with a large, centered title and subtitle.

### quirks
if the [`toc] extension is active but [`%[*toc]] directive is provided, the table of contents will be given its own section at the start of the document (after the title page, if any).

## further directions

### additional backends
it is eventually intended to support to following backends, if reasonably practicable.
* [*html]: emit HTML and CSS code to typeset the document. [!in progress]
* [*svg]: emit SVG, taking advantage of its precise layout features to produce a nicely formatted and paginated document. pagination can be accomplished through emitting multiple files or by assigning one layer to each page. [!long term]
* [*groff]: the most important output backend, rivalling [*html]. will allow the document to be typeset in a wide variety of formats, including PDF and manpage. [!short term]
* [*gemtext]: essentially a downrezzing of cortav to make it readable to Gemini clients
* [*ast]: produces a human- and/or machine-readable dump of the document's syntax tree, to aid in debugging or for interoperation with systems that do not support `cortav` direcly. mode [`ast:repr] wil allow selecting formats for the dump. [`ast:rel] can be [`tree] (the default) to emit a hierarchical representation, or [`flat] to emit an array of nodes that convey hierarchy [^flatdoc by naming one another], rather than being placed inside one another. [`tree] is easier for humans to parse; [`flat] is easier for computers. origin information can be included for each node with the flag [`ast:debug-syms], but be aware this will greatly increase file size.
** [`tabtree] [!(default)]: a hierarchical tree view, with the number of tabs preceding an item showing its depth in the tree
** [`sexp]
** [`binary]: emit a raw binary format that is easier for programs to read. maybe an lmdb or cdb file?
** [`json]

	flatdoc: ~~~flat sexp example output [scheme]~~~
		(nodes
			(section (id . "section1")
				(anchor "introduction")
				(kind . "ordinary")
				(label . "section1-heading")
				(nodes
					"section1-heading"
					"para1"
					"para2"
					"hzrule"
					"para3"))
			(section (id . "section2")
				(kind . "ordinary")
				(label . "section2-heading")
				(nodes
					"para4"
					"hzrule"
					"para5"
					"list1"))
			(block list (id . "list1")
				(kind . "ordered")
				(nodes
					"para6"
					"list2"
					"para7"))
			(block list (id . "list2")
				(kind . "unordered")
				(nodes
					"para8"
					"para9"
					"para10"))
			(block para (id . "para1")
				(nodes "text1" "format1" "text3" "foonote1" "text4"))
			(block label (id . "section1-heading") (nodes "section1-heading-text"))
			(text (id . "section1-heading-text") "Contemplating the Anathema")
			(text (id . "text1")
				"Disquieting information has recently been disclosed to virtual journalists of the Giedi Prime infomatrix by sources close to the Hyperion Entity regarding the catatrophic Year of Schisms and the unidentified agents believed to be responsible for memetically engineering the near-collapse of the Church Galactic.")
			(span format (id . "format1")
				(style . "emph")
				(nodes . "text2"))
			(text (id . "text2") "Curiously,")
			(text (id . "text3") "his Cyber-Holiness")
			(text (id . "footnote1-caption-text") "Pope Chewbacca III")
			(span footnote (id . "footnote1")
				(note . "footnote1-text")
				(ref . "papal-disclaimer")
				(nodes
					"footnode1-caption-text"))
			(text (id . "text4") "has thus far had little to say on the matter, provoking rampant speculation among the faithful.")
			(footnote-def (id . "footnote1-def")
				(nodes "footnote1-text")
			(text (id . "footnote1-text") "Currently recognized as legitimate successor to Peter of Terra by 2,756 sects, rejected by 678 of mostly Neo-Lutheran origin, and decried as an antipope by 73, most notably Pope Peter II of Centaurum Secundus, leader of the ongoing relativistic crusade against star systems owned by Microsoft.")
			;;; snip ;;;
			(document
				(nodes
					"section1" "section2")))
		~~~

some formats may eventually warrant their own renderer, but are not a priority:
* [*text]: cortav source files are already plain text, but a certain amount of layout could be done using ascii art.
* [*ansi]: emit sequences of ANSI escape codes to lay out a document in a terminal-friendly way
* [*tex]: TeX is an unholy abomination and i neither like nor use it, but lots of people do and if cortav ever catches on, a TeX backend should probably be written eventually.

PDF is not on either list because it's a nightmarish mess of a format and groff, which is installed on most linux systems already, can easily generate PDFs

### LCH support
right now, the use of color in the HTML renderer is very unsatisfactory. the accent mechanism operates on the basis of the CSS HSL function, which is not perceptually uniform; different hues will present different mixes of brightness and some (yellows?) may be ugly or unreadable.

the ideal solution would be to simply switch to using LCH based colors. unfortunately, only Safari actually supports the LCH color function right now, and it's unlikely (unless Lea Verou and her husband manage to work a miracle) that Colors Level 4 is going to be implemented very widely any time soon.

this leaves us in an awkward position. we can of course do the math ourselves, working in LCH to implement the internal [`@tone] macro, and then "converting" these colors to HSL. unfortunately, you can't actually convert from LCH to HSL; it's like converting from pounds to kilograms. LCH can represent any color the human visual system can perceive; sRGB can't, and CSS HSL is implemented in sRGB. however, we could at least approximate something that would allow for perceptually uniform brightness, which would be an improvement, and this is probably the direction to go in, unless a miracle occurs and [`lch()] or [`color()] pop up in Blink.

it may be possible to do a more reasonable job of handling colors in the postscript and TeX outputs. unsure about SVG but i assume it suffers the same problems HTML/CSS do. does groff even support color??

### intent files
there's currently no standard way to describe the intent and desired formatting of a document besides placing pragmata in the source file itself. this is extremely suboptimal, as when generating collections of documents, it's ideal to be able to keep all formatting information in one place. users should also be able to specify their own styling overrides that describe the way they prefer to read [`cortav] files, especially for uses like gemini or gopher integration.

at some point soon [`cortav] needs to address this by adding intent files that can be activated from outside the source file, such as with a command line flag or a configuration file setting. these will probably consist of lines that are interpreted as pragmata. in addition to the standard intent format however, individual implementations should feel free to provide their own ways to provide intent metadata; e.g. the reference implementation, which has a lua interpreter available, should be able to take a lua script that runs after the parse stage and generates . this will be particularly useful for the end-user who wishes to specify a particular format she likes reading her files in without forcing that format on everyone she sends the compiled document to, as it will be able to interrogate the document and make intelligent decisions about what pragmata to apply.

intent files should also be able to define [>rsrc resources], [>ctxvar context variables], and macros.